The present disclosure relates to a conductive roller which contacts with an image carrier while being used, and an image forming apparatus including the conductive roller.
Conventionally, there is known an image forming apparatus, such as a copier, printer, or facsimile, that is based on the electrophotographic method. The image forming apparatus includes: a drum-type photoreceptor (image carrier); and a charging device, exposing device, developing device, transfer device and the like that are arranged along the outer circumferential surface of the photoreceptor. A general image forming process performed by the image forming apparatus is as follows. First, the charging device charges the surface of the photoreceptor to a predetermined potential (hereinafter also referred to as “charging bias”), and subsequently the exposing device irradiates a laser beam onto the surface of the photoreceptor. This causes an electrostatic latent image to be formed on the surface of the photoreceptor, due to the difference in potential between the portions to which the laser beam has been irradiated, and the other portions. The developing device subsequently adheres toner, which has been charged to a potential higher than the potential of the electrostatic latent image, to the electrostatic latent image. After this, the transfer device gives charge, which has a polarity that is opposite to the charging bias, to the rear surface of a sheet of material having been transported to a predetermined transfer position, thereby transferring a toner image onto the surface of the sheet of material.
As the above-mentioned charging device, there is known a charging roller that conducts a voltage to the surface of the photoreceptor by contacting with the surface of the photoreceptor. The charging roller includes: a roller body that is made of a conductive rubber material and has a cylindrical shape; and a spindle that is current conductive and provided in the center of the roller body. For the photoreceptor to be charged uniformly without unevenness, the surface of the charging roller is required to have high flatness. However, it is difficult for the machining technology to manufacture a charging roller whose surface has high flatness. In particular, cutter blades or the like are used to cut the material into a predetermined size, the cut portions becoming the opposite ends in the axis direction of the roller body. In this cutting process, the opposite ends of the roller body may be influenced by the elasticity of the rubber material of the roller body and the opposite ends of the roller body may be swollen. When the charging roller with swollen ends contacts with the photoreceptor, the ends of the charging roller are pressed harder to the photoreceptor than the other portions of the charging roller. As a result, the photoreceptor is not charged uniformly. With regard to this problem, a typical mechanism is known that can reduce the pressing force of the ends of the charging roller that presses the photoreceptor when the charging roller contacts with the photoreceptor.